New Delhi: NIA has arrested a Kashmiri medical student who is alleged to be a 'key link' in the conspiracy behind the Delhi High Court blast last month that left 15 people dead and over 70 injured.

Wasim Ahmed, a student of Unani medicine in Bangaldesh, was being questioned by the NIA in connection with the blast, official sources said.

There was no official word on whether Wasim was arrested near the Indo-Bangla border or the authorities in Dhaka had handed him over.

Of the three people arrested earlier by the NIA in connection with the Delhi blast, one has been let off.

Wasim was also quizzed about the whereabouts of Hizbul Mujahideen operative Junaid Akram, believed to be one of the key conspirators in the Delhi blast, the sources said.

From the leads emerging in the case so far, the investigators suspect that it could be the handiwork of Pakistan-based terror outfit Hizbul Mujahideen and not Harkat-ul-Jehad-Islami (HuJI) as believed earlier.

Information about Wasim was given by Azhar Ali, an overground worker of Hizb, who is in Kotbalwal Jail in Jammu since 2009, the sources said.

An NIA team had questioned Ali, arrested for being allegedly involved in recruiting people from Kishtawar area besides securing SIM cards for the outfit, to know about some of the youths including Akram he had allegedly sent for training to Pakistan-occupied-Kashmir, the sources said.

Though NIA claimed that Akram was in Pakistan, sources in the security agencies believed that he was very much in Jammu and Kashmir.

NIA has arrested Abid Abbas, a high school boy, on charges of having sent an email after the September 7 Delhi High Court blast.

The probe agency had detained Abbas's brother from Shillong who expressed complete ignorance about the matter.